Flush toilets have been known in which the toilet body is flushed using flush water stored in a reservoir tank apparatus. A discharge valve apparatus is used on this reservoir tank apparatus; an example of a discharge valve apparatus is a discharge valve apparatus in which a discharge opening is opened and closed by moving a valve body up or down in the vertical direction relative to a discharge opening in a flush water tank. A known such discharge valve apparatus is one in which a float for causing buoyancy to act on a valve body is integrally formed with the valve body (e.g., see U.S. Pat. No. 8,079,095 (Document 1)).
In the conventional discharge valve apparatus, the valve body drops in the vertical direction in tandem with the descent of the water level inside the flush water tank, hence the time during which the discharge opening is opened by the valve body can be kept essentially constant, and the water level following completion of water discharge (the “dead water level” below) is stable.